Law of Chaos
by Tirainy
Summary: There used to be a single fundamental truth in Shadow's life that he has never expected to be proven to actually be an incorrect hypothesis. But then again 'impossible' has never been a legitimate word in Sonic's vocabulary. Future!fic


**To Captain:** Yes, I do plan to write longer stories. I just figured that I should finish Deepest Desire before tackling another big project. Though at the speed I'm going I guess I could try to write something else in the meantime.

 **To Just someone:** This was planned as one shot. But I'm happy to hear you enjoyed it so much to want another chapter!

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 **Law of Chaos**

There used to be a single fundamental truth in Shadow's life that he has never expected to be proven to actually be an incorrect hypothesis. But then again 'impossible' has never been a legitimate word in Sonic's vocabulary. Future!fic

 **TAGs:** Established Relationship, sonadow, one-shot, Writing Exercise, Wordcount: 1.000-5.000, fluff, future fic

 **Disclaimer: I do not own any of the characters from the Sonic the Hedgehog franchise.**

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"Man, what a night," Sonic slumps on the sofa beside Shadow, leaning against him tiredly, the blue spiky head coming to rest on the dark shoulder. A sigh leaves the weary speedster as he lets himself sink fully against his partner. "I'm spent."

"From what?" Shadow cocks an amused brow, wrapping an arm around the other's tired form, doing nothing to mask his own exhaustion. "Last time I checked _I_ was the one who had been organizing this whole party."

"...From being the best host imaginable while you handled all the technicalities," Sonic replies with a grin as he twists slightly to place a gentle kiss to the edge of his mouth, then the hero settles back into the proper position for using him as his personal pillow. "But thank you, Shadow. It was nice to see everyone again."

"Glad to hear you had fun." Shadow smiles as he presses a kiss behind the blue ear, drawing a pleased hum from the hero with the action, the sound intensifying when he also starts to lazily rub the other's side. "Anything else you'd like?"

Sonic hums thoughtfully. "...Pass me the cake. I haven't had the chance to enjoy it properly while I was talking to others."

Without a word, Shadow reaches for the plate with the white and blue birthday cake, for the briefest of moments finding himself staring at the wax numerals that rest atop of what remains of the cake, willing them to change or disappear like a mirage when you get too close to it, but the number-shaped candles do neither, unchanging and indisputable in their presence.

The agent's hand clutches tightly on the edge of the plate as he picks it up. He knows that number is right, hell, he _knows_ because it's literally been _decades_ since he and Sonic first crossed paths but that still doesn't make the thought any less ridiculous to him when he _looks_ at the hedgehog beside him, Sonic looking not even a day older than twenty-five—if even that—when everyday he _sees_ him walking with the same bounce in his step he's had since he was a teenager, the same wide radiant smile on his lips and the same playfulness in his eyes. When he _recalls_ how out of place Sonic had looked talking in the midst of his oldest friends just hours prior, with his youthful features unaffected by the passage of time, with his exaggerated hand-movements full of barely contained energy and the weight of age obviously missing from his body.

And yet that doesn't change the fact that Sonic has turned fifty today. _Fifty._

Lips pressing into a thin line, Shadow passes the plate to Sonic. The hero immediately digs in, a big smile spreading across his face at the delicious taste. "Yup. As I thought; it's even better than last year. Man, I should have let you make my birthday cakes since the start." Sonic smiles widely giving him a quick 'thank you' kiss before returning to the cake. "You know, Shad, if you ever feel like trying out a different career, baking could just be the thing for you."

Shadow hums in acknowledgement as he continues to silently stare at the wax numerals thoughtfully until Sonic finishes, sets the plate back on the table and looks at him with those big welcoming emerald eyes. There's maturity and shadows of hard times in them that show Sonic's older than he seems but apart from them, there is nothing else marking the hero's age to the outside world.

Shadow knows this state of things should please him, that he should be _happy_ about it—for Sonic at least. Sonic has always lived an active lifestyle so the longer his body serves him without any trouble, the better.

Because Sonic simply _refuses_ to let go of this aspect of his life; even when Dr. Eggman passed away and Sonic had the chance to finally slow down—and settle as many of his friends expected of him at that point—but, Sonic being Sonic, instead threw himself into working as a police officer, wanting to remain a crime-fighter and keep on making the world a better place. However, this particular career lasted only a couple of months before Sonic figured being a regular cop just wasn't for him and instead joined the GUN, which apparently was an idea his boss at the time was completely on board with as she felt Sonic's valuable skills and experience would be used to their full extent there.

It was actually during this time that he and Sonic grew close, the hero being assigned to him as a substitute partner for team missions while Rouge was on maternity leave. At first he had been unsure whether they wouldn't end up clashing like back in the old days but they quickly learned how to smoothly work together; Shadow supposed that was mostly thanks to him no longer being such a jerk like when they were teenagers and Sonic luckily not being one to hold grudges. It took them some time but after a lot of talking, joking and even arguing they eventually became friends and, in field, a pretty formidable duo.

Shadow honestly isn't sure who started flirting first, if him or Sonic—he believes Sonic—but once they started, they just couldn't stop. For a while they just kind of danced around one another, trying to figure whether the other was serious or just having fun but eventually Shadow did take the first step and asked Sonic out with "I'm tired of this game. Do you want to go to the dinner or not?", to which the hero responded with a laugh and something along the lines of "Oh? _You_ are already tired? Man, have I become more patient or you impatient?" but Sonic _did_ agree to the date that was the start of their now almost two decades long relationship—

There's a sharp jab to his side. "—bius to Shadow! You still with me?" Blinking awake, Shadow snaps for him musings, turning to look at his partner, who's now staring at him with a questioning expression on his face, one of his eyebrows raised curiously. "Is something wrong?"

"...I was just thinking," Shadow replies simply, not really sure for how long he's been zoning out. "About old times."

"Yeah, a lot of people were doing that today," Sonic comments as he reaches for a book that is laying on the coffee-table, the hero resting it in his lap. It takes Sonic flipping open the book for Shadow to realize it's, in fact, a photo-album. An old one as it seems. "Tails was showing the kids some photos from back when we used to fight to Eggman," Sonic explains as he flips to one of the photos that, judging by all the ruins around and the heroes looking a bit worse for wear, was taken in some post-victorious moment. Both Sonic and Tails are already adults in the photo, the two laughing even despite their injuries and Sonic hanging onto the other's shoulder; unsurprisingly, Tails outgrew Sonic by about a foot, which, however, Sonic never let stop him from calling Tails his 'little bro' to the inventor's displeasure.

Sonic sighs. "It's crazy how fast time passes. It still feels like yesterday when we were running, spoiling Eggman's plans."

"It does." Shadow affirms, the striped arm around Sonic's mid-section tightening ever so slightly as crimson eyes turn from the photo to instead once again gaze at the hero. It's crazy how fast time passes, but to him is even crazier how Sonic seems to defy it. While Tails has clearly changed since the day the photo was taken, Sonic still looks very much the same.

Shadow knows that some people are just lucky to win the gene lottery and have their body age at much slower rate than the rest of the populace. However, in Sonic's case it seems as if he's just stopped aging _completely_ , as if something decided he ought to remain eternally youthful.

Just like Professor Gerald decided for him, the Ultimate Life form.

But Sonic isn't an Ultimate Life Form, he's a mere Mobian and his body should not be capable of this feat. Especially not with the kind of life Sonic lives—the stress of hard life always reflects in the body as the lines of age or injuries that will never heal. But Sonic has neither; no lines of age and his body shows no signs of wear from the decades of constant hard use. Even many of the uncountable number of scars Sonic has collected seem to instead be fading into non-existence rather than remain and stack onto each other as years come.

Shadow knows he should be happy for Sonic. However, Shadow has come to terms that he's going to out-live everyone else long before he started dating Sonic, has accepted the fact he'll have to watch Sonic age and eventually die and that not happening is just...baffling and slightly unsettling. A mystery he cannot figure out no matter how hard he tries.

"Look how cute Tails used to be!"

Jerking a bit at the sudden noise, Shadow snaps back into the present and realizes he's once again let himself get lost in thought. It doesn't seem Sonic has noticed this time though.

"Don't you think Tails used to be cute?" Sonic asks again, this time turning to him with a grin. Shadow's gaze immediately drops back to the photo-album, looking at the picture the hero's pointing at. It's once again a picture of Sonic and Tails this time much _much_ younger. He guesses Tails to be maybe five years old in the picture and Sonic...twelve? He looks twelve.

Shadow's brows furrow in confusion as he continues to study the photo. "Are your eyes brown?"

"Well, yeah. I actually used to have dark brown eyes, you know? But when I turned 13 they started to turn green for some reason." Sonic grins as he leans against Shadow's side more. "But, hey, it happens to some people and it didn't cause me any problems, so I didn't think much about it."

Tan lips pull into a frown. It's true that person's eye color can change with age, just like the color of hair or fur, it's a natural process—

"You know, I think my eye-sight actually got better after my eyes turned green."

—but that isn't.

"Your eye-sight got better after your eyes turned green?" Shadow repeats, the metaphorical wheels in his head starting to turn once again. Hedgehog's bad eye-sight is notoriously known—Amy is a prime example of why—and until now he has never heard about anybody improving it without some kind of medical procedure being involved.

"Yeah, not by much, but it did. I'm able to see things sharper now than I used to as a kid. But, hey, my overall health and senses have improved after I started fighting with the Doc's robots, I guess that might have helped as well." Sonic shrugs his shoulders. "Tails once suggested it might have something to do with me turning super so many times. All that excess chaos energy making, well, _chaos_ in my body and all."

Sonic laughs a little but Shadow doesn't join him, his mind preoccupied with sorting out the new information that has been presented to him.

Chaos energy can both destroy and heal, can be both fuel and a tool, can be tamed to one's will and can be formidable force if let loose. It can control the flow of time and can warp space and maybe, just maybe also change the matter itself? Sonic's eyes turned green because of chaos...has chaos changed his very genetic code? Improved upon it? Has it changed any other aspect of his DNA? Is chaos the reason behind Sonic no longer aging?

Has chaos made Sonic..?

"Sonic?" Shadow asks, trying to keep both his tone and body calm. If he's right... "I'd like to try something."

"Hmm?" Sonic looks up from the photo-album, raising a curious eye-ridge. "Sure. What is it?"

"I want to try something with your chaos energy." Why does his throat have to feel so tight so suddenly? He gulps down to remove the feeling. "Just try to keep calm and not fight it, alright?"

The green eyes are big and questioning, wheels clearly turning in the other's head as the hero studies him, but Sonic doesn't voice any of his curiosity just yet. "Okay," the hero just says, letting his body fully slacken against Shadow's own, knowing that he needed to be relaxed for this. "Start whenever you want."

Taking a deep breath, Shadow allows his chaos energy seep from his hand where it's holding onto Sonic's side, guiding it to pass through Sonic's own skin into the hero's body where it's immediately met with Sonic's own warm chaos, which luckily doesn't offer any resistance to the intrusion like he's worried it would; though he supposes that is thanks to the years of healing each other's injuries that has made their bodies acquainted with each other's chaos enough to know it meant no harm.

Closing his eyes, Shadow concentrates on feeling the other's chaos, letting it communicate with his own, focusing on categorizing all the incoming sensations to learn whether his hypothesis is correct.

The moment Sonic's chaos hums in agreement, Shadow feels all kinds of emotions flooding his being, overwhelming him with their intensity. Before he can even try to reconquer the control over his body, he's already upon Sonic, caging his partner against the couch as he kisses the other with fervent need and uncontainable joy to which Sonic understandably replies with a muffled surprised yelp and then a push.

It takes Sonic three pushes to dislodge him from his lips. "Chaos, what's gotten into you?!" Sonic stares at him with wide eyes, clearly completely caught of guard by his sudden attack. To be honest, Shadow is kind of himself. "Not that I'm complaining," the hero adds quickly, the green eyes sweeping over his features to find some kind of clue why he's pounced on him so suddenly. "But really, what's going on?"

"You're _da_ _mn_ perfect that's what's happening," Shadow blurts out, his brain at the moment refusing to offer a more substantial answer as the agent is honestly feeling like he's riding some kind of high with the feeling of euphoria clouding his mind and his body buzzing with barely contained happiness.

He's not going to be alone. He's _not_.

Understandably, Sonic just blinks owlishly. "...I think I'll need _a bit_ more explanation than _that_."

Shadow starts opens his mouth but then clasps it shut again when he realizes that his finding might actually not be such a good news to Sonic. He himself has always though of his immortality as burden until now but that was because he thought it would inevitably leave him _all_ alone. However, eternity doesn't sound as daunting if he is to have Sonic by his side for the duration of it...

Mind running thousand miles per hour to figure out how exactly break it to Sonic, Shadow takes a deep breath and open his mouth to speak, hoping that Sonic, unlike himself, will see immortality as an opportunity rather than burden...


End file.
